A school has 9 periods a day each of 40 minutes duration. How long would each period be, if the school has 8 periods a day, assuming the number of school hours to be the same?
Lesser the number of periods in a day, more the duration of them. So, it is an inverse proportion.
Let the required duration be x.
⇒ 9 × 40 = 8 × x
⇒ x = = 45 days